Copper-loaded polymeric magnetic nanocatalysts as retrievable and robust heterogeneous catalysts for click reactions

Article abstract of DOI:10.1039/c4nj02134g

A novel heterogeneous copper catalyst based on poly(ionic liquid)-coated magnetic nanoparticles was prepared by the polymerization of 3-carboxymethyl-1-vinylimidazolium in the presence of surface-modified magnetic nanoparticles, followed by the coordinati

Full text of DOI:10.1039/c4nj02134g

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Copper-loaded polymeric magnetic nanocatalysts
as retrievable and robust heterogeneous catalysts
for click reactions†
Cite this:DOI: 10.1039/c4nj02134g
Ali Pourjavadi,*a Mahmood Tajbakhsh,*b Maryam Farhangb and
Seyed Hassan Hosseinia
A novel heterogeneous copper catalyst based on poly(ionic liquid)-coated magnetic nanoparticles was
prepared by the polymerization of 3-carboxymethyl-1-vinylimidazolium in the presence of surface-
modified magnetic nanoparticles, followed by the coordination of the carboxylate units in the polymer
chains with copper sulfate. The resulting catalyst has a high level of loading of copper ions and is used in
low weight percent. The catalytic activity of the newly designed catalyst was tested in a one-pot synthesis
of 1,4-disubstituted 1,2,3-triazoles by click reactions between primary halides or tosylates, sodium azide
and terminal acetylenes at room temperature in aqueous media. The unique nanocatalyst structure and
the multi-layered form of coated polymer on the magnetite surface are responsible for the excellent
catalytic performance for click reactions.
Received (in Porto Alegre, Brazil)
25th November 2014,
Accepted 9th March 2015
DOI: 10.1039/c4nj02134g
www.rsc.org/njc
of Cu(I) salts by Sharpless et al. led to a major improvement in
Introduction
both the rate and regioselectivity of the reaction.6 On the other
A challenging task in chemistry is the development of practical hand, copper salts as a homogeneous catalyst has many problems
methods, reaction media, conditions, and utilization of materials such as difficult separation and recycling of the catalyst, cytotoxi-
based upon the principles of green chemistry. The concept of city and environmental pollution. The removal of trace amounts
‘‘Green Chemistry’’ has emerged as one of the guiding principles of catalyst from the final product is essential because metal
of environmentally benign synthesis.1 The use of aqueous media contamination is highly regulated, particularly in the pharma-
in transition-metal catalyzed reactions has become popular2 ceutical industry. Even with the extensive methods, the elimina-
because water is non-toxic, non-flammable and easily available, tion of trace amounts of catalyst is a challenge.7
and water-based synthetic processes are inherently safer as well
as inexpensive. Moreover, the products can be separated easily can mitigate these problems. Recently, several methods have
by extraction. been developed to immobilize copper species on a large variety
Immobilization of homogenous catalysts on solid materials
1,2,3-Triazole derivatives are an important class of organic of solid supports. The major problems with using hetero-
compounds for medicinal chemistry, and exhibit a wide range geneous catalysts could be due to the low loading of the
of biological properties such as antiepileptic, anti-allergic,3 homogeneous catalyst onto the solid bed. In the normal grafting
anticancer and anti HIV properties.4 In general, these com- of organic compounds onto solid substrates, usually one layer of
pounds are prepared through Huisgen dipolar cycloaddition of organic compound is coated on the surface. Therefore, a large
organic azides and alkynes.5 However, because of the high amount of solid catalyst is needed for the catalytic process. On
activation energy (ca. 24–26 kcal molꢀ1), these cycloadditions the other hand, the use of a large amount of heterogeneous
are often very slow even at elevated temperatures (80–120 1C for catalyst causes more pollution of the reaction medium, and
12–24 h) and produce mixtures of regioisomers. The introduction requires more solvent for separation and recovery of catalyst.8–18
Among the various supports, Fe3O4 nanoparticles can facilitate
a Polymer Research Laboratory, Department of Chemistry, Sharif University of
Technology, Tehran, Iran. E-mail: purjavad@sharif.edu; Fax: +98 2 166165311;
Tel: +98 2 166165311
b Organic Chemistry Laboratory, Faculty of Chemistry, University of Mazandaran,
Babolsar, 47415, Iran. E-mail: Tajbakhsh@ac.ir; Fax: +98 2 166165311;
Tel: +98 2 166165311
the convenient removal and recycling of the magnetized catalyst
from the solution system without the need for any filtration or
centrifugation processes.19 The use of magnetic nanoparticles
(MNPs) has appeared as an ideal solution to the abovestated
problems.20–23
In this paper, we report the preparation and characterization
of a novel heterogeneous copper catalyst based on Fe3O4
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4nj02134g
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nanoparticles coated by multiple layers of poly functionalized by ultrasonication, and then an NH4OH solution (0.2 mL) was
vinyl imidazolium ionic liquid (IL). This catalyst efficiently pro- added into the flask. Next, excess amount of 3-(trimethoxysilyl)
moted the Huisgen 1,3-dipolar cycloaddition of organic azides propylmethacrylate (MPS) (4 mL) was added dropwise and
and terminal alkynes. At the end of the reaction, the catalyst is the mixture was stirred at 60 1C for 48 h. The MPS coated
easily separated by an external magnet, without using extra magnetic nanoparticles (MNPs@MPS) were magnetically sepa-
organic solvents or additional filtration steps and can be reused rated and washed several times with ethanol and dried at 50 1C
without the loss of catalytic activity or leaching of copper species. for 12 h.23
Synthesis of [VIM-COOH][Cl] monomer and cross-linker
BVD. Chloroacetic acid (2.82 g, 30 mmol) was dissolved in
toluene (300 mL), and 1-vinylimidazole (2.82 g, 30 mmol) was
added to the solution and the mixture was refluxed for 24 h.
Experimental
Reagents and analysis
Then, the reaction mixture was cooled to room temperature,
Chemical materials were purchased from Merck and Aldrich
and the liquid was poured out, and the solid was washed
Chemical Companies in high purity. All the solvents were
three times with acetonitrile (20 mL) to remove the unreacted
distilled, dried and purified by standard procedures.
starting materials. After drying in a vacuum for 24 h, a light
Melting points were measured on an Electrothermal 9100
yellow solid was obtained as IL monomer [VIM-COOH][Cl]
apparatus. The samples were analyzed using Fourier transform
(5.1 g, 90% yield).
infrared (FTIR) spectroscopy (ABB-Bomem MB-100 in KBr matrix).
For the preparation of 1,4-butane-diyl-3,30-bis-1-vinylimid-
The X-ray powder diffraction (XRD) of the catalyst was carried
azolium dibromide (BVD) as a cross-linking agent, 1-vinylimidazole
out on a Philips PW 1830 X-ray diffractometer with a CuKa
source (l = 1.5418 Å) in a range of Bragg’s angles (10–801) at
(2.82 g, 30 mmol) and 1,4-dibromobutane (13 g, 60 mmol) were
stirred in methanol at 60 1C for 20 h. The reaction mixture was then
room temperature. Scanning electron microscopy (SEM) images-
cooled to room temperature and added to diethyl ether (250 mL).
EDS analyses were obtained using a VEGA//TESCAN KYKY-
The resulting translucent solution was placed in a refrigerator
EM3200 microscope (acceleration voltage 26 kV). Transmission
for 5 h. Solid products were separated by the decantation of
electron microscopy (TEM) experiments were conducted on a
supernatant, washed three times with diethyl ether, and dried
1
Philips EM 208 electron microscope. H and 13C NMR spectra
under vacuum at 50 1C for 12.24a
were recorded on a BRUKER DRX-400 AVANCE spectrometer.
Mass spectra were recorded on a FINNIGAN-MATT 8430 mass
Synthesis of catalyst (MNP@ImAc/Cu). MNP@MPS (0.5 g),
[VIM-COOH][Cl] (1 g) and BVD (0.4 g) were loaded into a 100 mL
spectrometer operating at an ionization potential of 20 eV.
round bottom flask and methanol (40 mL) was added. The
Elemental analyses for C, H and N were performed using a
mixture was sonicated for 20 min, and then deoxygenated
Heraeus CHN-O-Rapid analyzer. Thermogravimetric analysis
under argon for another 20 min. Subsequently, AIBN (5 mg)
(TGA) was recorded on a Stanton Redcraft STA-780 (London,
was added to the mixture and the flask was equipped with a
UK). Magnetic measurements were performed using vibration
sample magnetometry (VSM, MDK, and Model 7400) analysis.
A simultaneous ICP-OES (Varian Vista-Pro, Springvale, Australia)
coupled to a V-groove nebulizer and equipped with a charge-
condenser and placed in an oil bath at 70 1C. After 24 h, the
solid products were magnetically separated, washed three times
with methanol, and dried under vacuum at 60 1C. For neutrali-
zation of the carboxylic acid groups within the polymer network,
coupled device (CCD) was applied for the determination of the
the powdered magnetic solid was dispersed in water (25 mL), an
trace metal ions.
excess of K2CO3 solution was added, and the mixture was stirred
for 20 h at room temperature. The obtained solid MNP@ImAc
was magnetically separated, washed three times with water, and
General procedure
Synthesis of vinyl-functionalized magnetic nanoparticles dried under vacuum at 60 1C for 12 h.
(MNPs@MPS)ꢁ. An iron salt solution was obtained by mixing
The obtained MNP@ImAc (0.5 g) was dispersed in deionized
FeCl3ꢂ6H2O (2.35 g, 8.7 mmol) and FeCl2ꢂ4H2O (0.86 g, water at room temperature, an aqueous solution of copper sulfate
4.3 mmol) in deionized water (40 mL). The resultant solution (1 M, 25 mL) was added to the mixture, and mixture was stirred
was allowed to stir for 30 min at 80 1C. Then, NH3 (25%, 5 mL) for 24 h at 50 1C. The resulting solid was magnetically separated,
was added with vigorous stirring to produce a black precipitate washed five times with water (5 ꢃ 20 mL), and dried under
and the reaction was continued for another 30 min. The pre- vacuum for 12 h to give MNP@ImAc/Cu.
cipitate was isolated by magnetic decantation, washed several
Determination of the copper content in MNP@ImAc/Cu.
times with deionized water, and then dried at 80 1C for 10 h. The MNP@ImAc/Cu (100 mg) was extracted with concentrated
Dried Fe3O4 nanoparticles (0.5 g) were suspended in a solution HCl (5 ꢃ 2 mL) in a screw-capped vessel, followed by treatment
of ethanol (50 mL) and NH3 (25%, 5 mL). Then, tetraethoxysilane with concentrated nitric acid (2 mL) to digest the metal com-
(TEOS, 0.2 mL) was added dropwise to the abovementioned plexes. The mixture was then transferred into a volumetric
suspension, and the mixture was ultrasonicated for two h. flask (100 mL), diluted 1:50 for the second time and analyzed
Subsequently, silica coated Fe3O4 (MNPs) were magnetically by inductively coupled plasma-optical emission spectrometry
separated, washed three times with ethanol and dried at 80 1C (ICP-OES) analysis.24b The loading of copper ion on the supported
for 10 h. MNPs (100 mg) were dispersed in dry ethanol (15 mL) catalyst was calculated to be 13.23 wt% (2.1 mmol gꢀ1).
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General procedure for the synthesis of 1,4-disubstituted
triazoles
layer of SiO2 was coated on the Fe3O4 surface to improve the
chemical stability and biocompatibility of the particles. Next, the
surface of MNP was modified with MPS (MNPs@MPS) to ensure
that MNPs were covalently bonded to the copolymer chains.
Copolymerization was initiated by AIBN and in the presence of
BVD as a cross-linker. During the polymerization, magnetic
nanoparticles were entrapped into the cross-linked polymer
matrix and covalently attached to the polymer chains. Using this
method, a multi-layered polymer is formed and envelopes the
magnetic nanoparticles. After the preparation of the solid support,
the carboxylic acid groups are neutralized by base. Then, copper
sulfate was loaded onto the support surface through strong
coordination with the numerous carboxylate groups.
Conventional immobilization of ionic liquids on support
surfaces usually leads to a low loading of the immobilized ionic
liquids, but in this method, the solid support is prepared using
ionic liquid monomers, which improves the loading level of
the supported catalyst. Actually, in this method the magnetic
nanoparticles are coated by several layers of polymer chains,
and a magnetic composite is formed. The resulting support has
numerous coordination sites, which can adsorb a large number
of copper ions and increase the loading level of copper on the
support surface.
Primary halides (1 mmol), NaN3 (1.2 mmol, 0.08 g) and terminal
alkynes (1 mmol) were placed in a 10 mL round-bottom flask in
H2O (3 mL). Sequentially, MNP@ImAc/Cu (1 mg, 0.2 mol%) and
sodium ascorbate (10 mol%, 0.02 g) were added to the solution.
The reaction mixture was stirred at room temperature and the
completion of reaction was monitored by TLC. After the comple-
tion of the reaction, the catalyst was magnetically separated and
washed several times with EtOH followed by water, and dried
under vacuum for 12 h. The residue was extracted with EtOAc
(2 ꢃ 10 mL), followed by drying with anhydrous Na2SO4. After the
evaporation of the solvent, the desired pure product was isolated,
and if necessary the product was further purified by recrystalliza-
tion using EtOAc–hexane mixtures or EtOH. The products were
1
characterized with IR, H NMR and 13C NMR spectroscopies.
Retreatment of recovered catalyst
After several cycles, when the reaction rates were reduced, the
recovered catalyst in the click reaction was retreated with the
copper sulfate solution. For this purpose, recovered catalyst
(0.05 gm) was stirred in an aqueous solution of copper sulfate
(0.1 M, 10 mL) at 50 1C for 6 h. The brown residue was
separated by an external magnet and washed with water several
times. The catalyst was dried for 24 h and reused in the next
reaction (Fig. 8, Regenerated catalyst).
Fourier transform infrared spectra (FTIR) help identify the
chemical bonds in the prepared samples. Fig. 2 shows the FTIR
spectra of bare MNPs (b), MNP@MPS (c), MNP@ImAc (d) and
MNP@ImAc/Cu (e). In the FTIR spectrum of MNPs (Fig. 2a), the
characteristic adsorption band of Fe–O is observed at 624 cmꢀ1
.
The broad band at 3300–3500 cmꢀ1 is due to –OH stretching
vibrations. The presence of the characteristic peak of Si–O at
1062 cmꢀ1 confirms the formation of the silica shell around the
Results and discussion
Fabrication of the catalyst
The synthesis of MNP@ImAc/Cu is shown in Fig. 1. Initially, Fe3O4 core. The characterization peaks of MNP are observed
the co-precipitation of FeCl3 and FeCl2 in an ammonia solution in all of the spectra, confirming the existence of MNPs in all
led to the formation of Fe3O4 nanoparticles (MNPs). Then, a samples. The FTIR spectrum of MNP@MPS (Fig. 2b) shows the
Fig. 1 Synthesis of the MNP@ImAc/Cu catalyst.
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250–600 1C corresponding to the thermal decomposition of the
grafted propylmethacrylate groups onto the MNP surface. From
this weight loss, the loading amount of MPS onto the MNP
surface was calculated to be 0.78 mmol gꢀ1. After polymeriza-
tion, the weight loss in MNP@ImAc/Cu increased again, which
was due to the thermal degradation of the polymeric content.
Based on the TG analysis, MNP@ImAc/Cu exhibited good thermal
stability under 300 1C. TGA pattern for MNP@ImAc/Cu (Fig. 3)
shows the drastic weight loss of nearly 44% at 250–500 1C for
the cross-linked polymeric network.
The average particle size and morphology of the nano-
particles were investigated by scanning electron microscopy
(SEM) and transmission electron microscopy (TEM). Fig. 4
presents the TEM images of MNP (a) and MNP@ImAc/Cu (b).
From the TEM image of MNP the size of the spherical magnetic
nanoparticles is around 7–15 nm. As shown in the TEM image
of MNP@ImAc/Cu, magnetic nanoparticles are embedded into
the polymeric matrix.
Fig. 2 FTIR spectra of (a) bare MNPs, (b) MNP@MPS, (c) MNP@ImAc and
(d) MNP@ImAc/Cu.
The scanning electron microscopy (SEM) image of MNP@
ImAc/Cu (Fig. 5) shows that the surface of the catalyst is rough
due to the presence of MNPs. This rough morphology of the
catalyst surface may improve the catalytic activity by increasing
the available catalytic sites. The energy dispersive X-ray spectro-
scopy (EDAX) analysis of MNP@ImAc/Cu (Fig. 5) confirms the
presence of copper and iron in the catalyst structure.
The magnetic properties of MNP (a) and MNP@ImAc/Cu (b)
were determined by a vibrating sample magnetometer (VSM),
and magnetic hysteresis curves are shown in Fig. 6. The VSM
curve for MNP@ImAc/Cu shows that its saturation magnetiza-
tion value was 29 emu gꢀ1 without the observation of hysteresis
curves, indicating the typical superparamagnetic behavior. The
saturation magnetization of MNP@ImAc/Cu is smaller than
that of bare MNPs due to the entrapment of MNPs into the
nonmagnetic materials. However, the magnetization is still
large enough for the separation of the catalyst.
The crystalline structures of prepared nanoparticles were
analyzed by X-ray powder diffraction (XRD). The XRD pattern of
MNPs (Fig. 7b) shows peaks at 2y values 30.11, 35.41, 43.11,
53.41, 571 and 62.61 related to the (220), (311), (400), (422), (511)
and (440) crystal planes of Fe3O4 cubic lattices, which agrees
well with the standard structure of Fe3O4 (JCPDS card no.
85-1436). The XRD pattern of MNP@ImAc/Cu (Fig. 7a) contains
the above peaks together with a broad peak from 201 to 301, which
could be assigned to the synergetic effect of amorphous silica.
All the data discussed above confirms that the magnetic
nanoparticles are embedded into the polyvinylimidazolium
chains and that a magnetic composite with a large number of
copper ions is formed.
strong stretching vibration bands of the carbonyl groups
(1714 cmꢀ1), CQC (1610 cmꢀ1) and C–H (2923 cmꢀ1), indicat-
ing that MPS was successfully attached to the surface of MNPs.
Fig. 2c shows the FTIR spectrum of MNP@ImAc with charac-
teristic peaks at 1561 cmꢀ1, 1630 cmꢀ1, and 1740 cmꢀ1, which
can be attributed to the C–N, CQN and CQO stretching
vibrations of the imidazole rings and –COOH groups, respectively.
This result shows that the solid magnetic support MNP@ImAc
was successfully prepared. In the spectrum of MNP@ImAc/Cu
(Fig. 2d), all the characteristic peaks of MNP@ImAc are observed.
Moreover, the stretching vibration band of SQO is observed at
1133 cmꢀ1, indicating that CuSO4 is successfully immobilized
on the support surface.
The results of elemental analyses of MNP@MPS, MNP@ImAc
and MNP@ImAc/Cu are tabulated in Table 1. A comparison
between the CHNS analysis of MNP@MPS and MNP@ImAc
shows that the content of C, H and N atoms increased in
MNP@ImAc, indicating that MNP@MPS was successfully coated
by polymer chains. The increase in sulphur content in MNP@
ImAc/Cu is attributed to the immobilization of CuSO4.
Thermogravimetric analysis (TGA) and derivative thermo-
gravimetric (DTG) analysis were performed in the range of 25 to
800 1C to determine the loading of organic groups coated onto
the surface of the magnetite. Fig. 3 shows the TGA and DTG
of MNP (a), MNP@MPS (b) and MNP@ImAc/Cu (c). In all the
samples, the weight loss within 100–200 1C is due to the
physically adsorbed water molecules and hydroxyl groups at
the magnetite surface. MNPs@MPS shows a 10% weight loss at
Catalytic Performance of MNP@ImAc/Cu
Table 1 Elemental analysis for the catalyst
The catalytic activity of MNP@ImAc/Cu was tested in the multi-
component 1,3-dipolar cycloaddition reaction of terminal
alkynes, sodium azide and alkyl halides or tosylates, along with
10 mol% of sodium ascorbate. The reaction of phenylacetylene
(1 mmol), benzyl bromide (1 mmol), NaN3 (1.2 mmol) and
sodium ascorbate (10 mol%) was chosen as a model reaction,
Samples
C%
6.15
H%
N%
S%
MNP@MPS
1.45
3.54
3.66
3.92
—
—
—
16.40
4.63
MNP@ImAc
MNP@ImAc/Cu
Recycled MNP@ImAc/Cu
25.32
24.13
25.76
8.61
8.02
7.87
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Fig. 3 (I): (a) TGA of MNP, (b) MNP@MPS and (c) MNP@ImAc/Cu; (II) DTG of MNP@ImAc/Cu.
Fig. 4 TEM images of (a) MNP and (b) MNP@ImAc/Cu.
and the reaction was examined in different conditions, and the
results are presented in Table 2. It can be seen that when the
model reaction was carried out at room temperature in aqueous
medium in the absence of any catalyst, no desired product was
Fig. 6 VSM curves of (a) MNP and (b) MNP@ImAc/Cu.
formed after 5 h (entry 1). Moreover, no significant product was reaction (entry 17). The model reaction was also carried out in
observed with bare MNP or MNP@ImAc as the catalyst in water the presence of MNP@IMAcCu(I) under the same reaction con-
after 5 h (entries 2 and 5). On the other hand, CuSO4 and CuSO4/ ditions, and the desired product was formed in 75% yield after
ImAc as homogeneous catalysts resulted in 15% and 65% yields 2 h (entry 18). This is in agreement with observations reported in
in water in 5 h (entries 3 and 4). However, using 3 mg MNP@ the literature that the catalytically active Cu(I) species directly
ImAc as the catalyst gave 99% yield in 1 h. Reducing the amount generated by reduction with ascorbate immediately forms
of catalyst demonstrates that 1 mg MNP@ImAc is enough for the Cu–acetylides, but CuCl salts require high temperatures to form
completion of the reaction (entries 6–9). Different solvents and the Cu–acetylide complexes.24c The results show that the highest
solvent–co-solvent mixtures were tested, and water was found yield of 1-benzyl-4-phenyl-1H-1,2,3-triazole was achieved with
to be the most effective medium for this reaction (entries 8 and 1 mg catalyst in water for only 1 h at room temperature (entry 8).
10–14). Increasing the reaction temperature to 70 1C reduced On the other hand, it is interesting to note that under these
the reaction time to 30 min for the completion of the reaction. conditions, no other byproducts were observed.
The absence of sodium ascorbate as a reducing agent of Cu II to
In order to explore the generality and applicability of this
Cu I clearly demonstrates the effect of sodium ascorbate in this catalyst, a variety of primary halides or tosylates with alkynes
Fig. 5 SEM image and EDAX analysis of MNP@ImAc/Cu.
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equivalents of phenylacetylene to give the bistriazole product.
Aliphatic alkynes, such as 1-heptyne also gave the expected
triazoles in good to high yields, although in longer reaction
times compared with their aryl counterparts.
To investigate the practical applicability of the catalyst in
scaled up reactions, the model reaction was repeated on a 20 mmol
scale under similar conditions as the optimized reaction. The
reaction proceeded well with 91% isolated yield in 1 h.
Reusability test of MNP@ImAc/Cu
For a heterogeneous catalyst, it is essential to study its ease of
separation, recoverability and recyclability. The reusability of
MNP@ImAc/Cu was investigated in the synthesis of 1,4-substituted
1,2,3-triazoles by choosing the reaction between benzylbromide,
phenylacetylene and sodium azide under the optimized reaction
conditions. After the completion of the reaction, the catalyst was
Fig. 7 XRD patterns of (a) MNP@ImAc/Cu and (b) MNP.
and NaN3 were reacted under the optimal reaction conditions easily removed using a magnet and recovered by washing with
and the results are summarized in Table 3. In all cases, the EtOH, and vacuum drying. The recovered catalyst was reused for
transformation regiospecifically provided the 1,4-substituted ten times without a significant decrease in catalytic activity (Fig. 8).
1,2,3-triazoles in satisfactory to excellent yields. Different benzyl However, after the fifth run, a longer reaction time was required
bromides reacted well with alkynes and NaN3 to afford the for the completion of the reaction, which is due to the mass loss
corresponding triazoles in nearly quantitative yields. In the case of catalyst during the separation and washing of the catalyst.
of activated functionalized organic halides such as p-bromo Therefore, by losing the mass of the catalyst, more time was
phenacyl bromide, phenacyl bromide, ethyl bromoacetate and required for the completion of the reaction. After several cycles,
acetamide bromide, the reactions smoothly proceeded and the when the reaction rates were reduced, the recovered catalyst was
products were isolated in high yields. Note that allyl bromide as retreated, and thus the regenerated catalyst resumed the initial
well as its benzyl counterpart reacted; moreover, it is clear that activity of the fresh one, showing conversion of 99% after
aliphatic alkyl bromides were tolerated as well. It was found 60 min. This demonstrates a good regenerative capability for
that terminal dibromoalkane (1,2-dibromoethane) reacts with 2 MNP@ImAc/Cu (Fig. 8, Regenerated catalyst).
Table 2 Optimization of the reaction conditions for the synthesis of 1,4-disubstituted 1,2,3 triazoles
Entrya
Catalyst
Cat. loading (Cu mol%)
Solvent
T
Time
Yieldb (%)
1
2
3
4
5
6
7
8
—
MNP
CuSO4
CuSO4/ImAc
—
3 mg
0.6
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
50 1C
70 1C
r.t
5 h
5 h
5 h
5 h
5 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
0.5 h
1 h
2 h
—
Tracec
15
0.6
65
—
99
99
99
82
91
30
MNP@ImAc
3 mg
3 mg, 0.6
0.4
0.2
0.1
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu
MNP@ImAc/Cu(I)e
9
H2O
10
11
12
13
14
15
16
17
18
H2O: EtOH
EtOH
THF
MeOH
Hexane
H2O
H2O
H2O
H2O
Trace
65
55
99
99
Traced
78
0.2
r.t
a
All of the reactions were carried out under the conditions: benzyl bromide (1 mmol, 0.12 mL), NaN3 (1.2 mmol, 0.08 g), phenylacetylene (1 mmol,
b
c
d
0.10 mL), solvent (3 mL) and sodium ascorbate (10 mol%, 0.02 g). Isolated yield. Mixture of 1,4- and 1,5-isomers. Without using sodium
ascorbate. MNP@ImAc/Cu(I)was prepared from MNP@ImAc and CuCl in H2O.
e
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Table 3 Huisgen 1,3-dipolar cycloadditions catalyzed by MNP@ImAc/Cua
Entry
Alkyne
Alkyl/aryl halide
Product
Time (h)
1
Yieldb (%)
99
1
2
3
4
2
1
1
93
99
97
5
6
7
3
3
3
91
90
93
8
9
5
3
98
92
10
2
94
11
12
13
14
2
1
3
2
96
99
97
89
15
5
88
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Table 3 (continued)
Entry
Alkyne
Alkyl/aryl halide
Product
Time (h)
5
Yieldb (%)
91
16
17
1
90
18
19
20
3
3
3
91
95
97
21
22
23
3
3
3
91
92
90
24
4
82
25
26
27
2
2
2
94
94
93
28
2
2
96
93
29
a
Reaction conditions: alkyne (1 mmol), primary halide or tosylate (1 mmol), NaN3 (1.2 mmol, 0.08 g), sodium ascorbate (10 mol%, 0.02 g),
b
MNP@ImAc/Cu (1 mg, 0.2 mol%), H2O (3 mL), r.t. Isolated yield.
To explore the catalyst leaching, the reaction between benzyl- catalyst was magnetically separated. The yield of product was
bromide, phenylacetylene and sodium azide was carried out measured by GC (68%). The residue was then allowed to react
under optimized conditions. After 30 min (half of needed time without catalyst for another 90 min. After that, the reaction
for completion of reaction) the reaction was stopped and the mixture was analyzed by GC and the result showed that no
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emission spectrometry (ICP-OES). The result of ICP-OES analysis
for the reaction mixture and product showed no copper species.
The results of CHNS analysis after catalyst recycling showed no
significant change in the C, H or N contents. However, after
recycling the sulfur atom content is reduced due to the exchange
of SO4ꢀ2 anions with ascorbate (Table 1). The content of copper
in the reused catalyst was analyzed by ICP-OES, and the result
showed no significant change in copper loading (13.12 wt%,
2.08 mmol gꢀ1 copper). The TEM image of the catalyst after
recycling shows no change in catalyst structure (Fig. S1, ESI†).
These results show that MNP@ImAc/Cu is highly stable, and the
catalyst is truly heterogeneous. Moreover, we have found that no
special handling precautions regarding exposure to air/moisture
need to be taken when using MNP@ImAc/Cu as a catalyst.
Comparison with other reported systems
Fig. 8 Recyclability of MNP@ImAc/Cu.
The performances of MNP@ImAc/Cu and previously reported
catalysts were compared in Table 4. Although all the methods
are effective, the present procedure comparatively affords a truly
green process with high yield of the products in shorter reaction
times at room temperature, and carries out these reactions in
water using magnetically separable nanoparticles as the catalyst.
It is worth noting that the loading amount of copper ions in
MNP@ImAc/Cu is relatively high. This property of the catalyst is
especially useful in large-scale applications, where the amount of
expensive catalyst should be low.
Conclusion
A novel copper magnetic catalyst based on poly(ionic liquid)
was synthesized and showed to be a highly efficient hetero-
geneous catalyst for the one-pot synthesis of 1,4-disubstituted
1,2,3-triazoles in water at room temperature without using any
toxic solvents or co-catalysts. This protocol is a clean and safe
process and can be used to generate a diverse range of products
Fig. 9 Catalyst leaching experiment.
significant conversion was observed after catalyst separation in good to excellent yields. Because of the polymeric nature
(Fig. 9). Moreover, the amount of metal loaded onto the surface of the coating material, the loading amount, recyclability and
was also measured by inductively coupled plasma-optical catalytic activity of catalyst is largely promoted. Moreover, this
Table 4 The comparison of MNP@ImAc/Cu with reported catalysts in the synthesis of triazolesa
Copper loading on catalyst
Catalyst loading
(mol%)
Catalyst
(mmol gꢀ1
)
Time (h)
T
Yield (%)
Ref.
Functionalized chitosan/Cu
Cross-linked polymeric ionic liquid/Cu
Ionic polymer/Cu
Poly(4-vinyl pyridine)/Cu
Nano ferrite–glutathione–copper
Poly(NIPAM/Im)/Cu
Poly(NIPAM/Im)/Cu
MNP–CuBr
Cu/Al2O3
Cu(II)/clay
Cu/SiO2
CuNPs/Magsilica
0.6
1.0
0.1
1.0
5
12
48
2.5
0.4
0.17
1.5
31
0.3
1
0.25
0.17
1
3
1
70 1C
r.t
r.t
99
98
99
89
99
99
94
96
92
98
92
98
98
99
25
26
27
28
7
29
29
21
9
0.25
1.32
0.25
0.46
0.46
0.44
0.29
1.5
2.59
1.07
0.25
2.1
13
100 1C
2.5
0.25
0.00045
1.46
10
2
10
4.3
0.5
0.2
120 1C, mwc
50 1C
50 1C
80 1C, mwc
r.t.
Sonic. r.t
70 1C or 50 1C, mwb
70 1C
70 1C
r.t.
10
30
30
31
Cu NP/activated carbon
MNP@ImAc/Cu
c
—
a
b
c
Click reaction of benzylbromide, sodium azide, and phenylacetylene. Microwave system. Present work.
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12 Y. Monguchi, K. Nozaki, T. Maejima, Y. Shimoda,
Y. Sawama, Y. Kitamura, Y. Kitade and H. Sajik, Green
Chem., 2013, 15, 490–495.
13 M. Nasr-Esfahani, I. Mohammadpoor-Baltork, A. R. Khosropour,
M. Moghadam, V. Mirkhani, S. Tangestaninejad and H. A.
Rudbari, J. Org. Chem., 2014, 79, 1437–1443.
nanocatalyst is stable showing no aggregation and copper
leaching and can be recycled many times without the loss of
catalytic activity. From the viewpoint of green chemistry, the
present protocol was proven to be useful and has been a
potential protocol for use in industrial applications.
´
14 I. Jlalia, F. Gallier, N. Brodie-Linder, J. Uziel, J. Auge and
Acknowledgements
N. Lubin-Germain, J. Mol. Catal. A: Chem., 2014, 393, 56–61.
15 Y. Kitamura, K. Taniguchi, T. Maegawa, Y. Monguchi,
Y. Kitade and H. Sajiki, Heterocycles, 2014, 88, 233–243.
16 L. Wan and C. Cai, Catal. Lett., 2012, 142, 1134–1140.
We are grateful for financial support by the Iran’s National
Elites Foundation.
´
17 I. Luz, F. X. Llabres, I. Xamena and A. Corma, J. Catal., 2010,
References
276, 134–140.
18 B. Dervaux and F. E. Du Prez, Chem. Sci., 2012, 3, 959–966.
19 J. Safari and Z. Zarnegar, C. R. Chim., 2013, 821–828.
20 F. Nador, M. A. Volpe, F. Alonso, A. Feldhoff, A. Kirschning
and G. Radivo, Appl. Catal., A, 2013, 455, 39–45.
21 X. Xiong and L. Cai, Catal. Sci. Technol., 2013, 3, 1301–1307.
22 P. Veerakumar, M. Velayudham, K. Lu and S. Rajagopal,
Catal. Sci. Technol., 2011, 1, 1512–1525.
1 A. S. Matlack, Introduction to Green Chemistry, Marcel Dekker,
New York, 2001.
2 H. Shintaku, K. Nakajima, M. Kitano, N. Ichikuni and
M. Hara, ACS Catal., 2014, 4, 1198–1204.
3 S. A. Bakunov, S. M. Bakunova, T. Wenzler, M. Ghebru,
K. A. Werbovetz, R. Brun and R. R. Tidwell, J. Med. Chem.,
2010, 53, 254–272.
23 A. Pourjavadi, S. H. Hosseini, F. Matloubi Moghaddam,
B. K. Foroushani and C. Bennett, Green Chem., 2013, 15,
2913–2919.
4 R. Alvarez, S. Velazquez, F. San, S. Aquaro, C. De, C. F. Perno,
A. Karlesson, J. Balzarini and M. J. Camarasa, J. Med. Chem.,
1994, 37, 4185–4194.
24 (a) J. Yuan and M. Antonietti, Macromolecules, 2011, 44,
744–750; (b) J. A. Albadi, M. Keshavarz, M. Abedini and
M. Khoshakhlagh, J. Chem. Sci., 2013, 125, 295–298;
(c) M. Melda and C. W. Tornøe, Chem. Rev., 2008, 108,
2952–3015.
25 M. Chtchigrovsky, A. Primo, P. Gonzalez, K. Molvinger,
M. Robitzer, F. Quignard and F. Taran, Angew. Chem.,
2009, 121, 6030–6034.
5 R. Huisgen, in 1,3-Dipolar Cycloaddition Chemistry, ed.
A. Padwa, Wiley, New York, 1984.
6 (a) V. V. Rostovtsev, L. G. Green, V. V. Forkin and
K. B. Sharpless, Angew. Chem., Int. Ed., 2002, 41, 2596–2599;
(b) C. W. Tornoe, C. Christensen and M. Meldal, J. Org.
Chem., 2002, 67, 3057–3064.
7 (a) R. B. Nasir Baig and R. S. Varma, Green Chem., 2012, 14,
625–632; (b) B. Dervauxa and F. E. Du Prez, Chem. Sci., 2012,
26 Y. Wang, J. Liu and C. Xia, Adv. Synth. Catal., 2011, 353,
1534–1542.
27 U. Sirion, Y. J. Bae, B. S. Lee and D. Y. Chi, Synlett, 2008,
2326–2330.
28 J. Albadi, M. Keshavarz, F. Shirini and M. Vafaie-nezhad,
Catal. Commun., 2012, 27, 17–20.
˜
3, 959–966; (c) A. Megia-Fernandez, M. Ortega-Munoz,
J. Lopez-Jaramillo, F. Hernandez-Mateo and F. Santoyo-
Gonzalez, Adv. Synth. Catal., 2010, 352, 3306–3320.
8 B. S. P. Anil Kumar, K. H. V. Reddy, B. Madhav, K. Ramesh
and Y. V. D. Nageswar, Tetrahedron Lett., 2012, 53,
4595–4599.
29 Y. M. A. Yamada, S. M. Sarkar and Y. Uozumi, J. Am. Chem.
Soc., 2012, 134, 9285–9290.
9 N. Mukherjee, S. Ahammed, S. Bhadra and B. C. Ranu,
Green Chem., 2013, 15, 389–397.
30 C. S. Radatz, L. d. A. Soares, E. f. R. Vieira, D. Alves,
D. Russowsky and P. H. Schneider, New J. Chem., 2014, 38,
1410–1417.
10 B. A. Dar, A. A. Bhowmik, A. Sharma, P. R. Sharma, A. Lazar,
A. P. Singh, M. Sharma and B. Singh, Appl. Clay Sci., 2013,
80–81, 351–357.
31 F. Alonso, Y. Moglie, G. Radivoy and M. Yus, Adv. Synth.
Catal., 2010, 352, 3208–3214.
11 A. Coelho, P. Diz, O. Caamaço and E. Sotelo, Adv. Synth.
Catal., 2010, 352, 1179–1192.
New J. Chem.
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